The Cadmium zinc telluride (CdZnTe) detector is a high-performance semiconductor radiation detector at room temperature (RTD) developed recently. The CdZnTe crystal is characterized of high resistivity (about 1011 Ωcm), a large atomic number, a wide bandgap (the bandgap varied continually from 1.4 eV to 2.26 eV), so that a detector manufactured from which has small leakage current, an excellent energy resolution for X and γ rays at room temperature, an energy detection range of 10 keV-4 MeV and has no polarization phenomena, and thus can be applied to various kinds of detectors and spectrometers in fields of astronomy, medical science, industry, military affairs, safety inspection and the like.
As compared with other semiconductors, such as a high purity germanium (HPGe), CdZnTe has a wider bandgap, a larger impendence, a lower intrinsic carrier density, and has smaller dark current when a bias voltage is applied onto two terminals thereof, thus being a semiconductor detector capable of operating under room temperature. Also as compared with a scintillator detector, the CdZnTe detector has a high energy resolution which is much better than that of a sodium iodide (NaI) detector, and the CdZnTe has no polarization effect, the signals detected by the detector are converted directly, and thus the detector is liable to combine with front-end electronics. A nuclear radiation detector made of CdZnTe has a small size, being portable and can operate under room temperature.
However, the performance of the CdZnTe detector is hindered due to certain defects existed in the CdZnTe crystal. In principle the μτ value of carriers in the CdZnTe crystal is lower and at the order of 10−5, and the mobility difference is significant between electrons and holes; the carrier lifetime of the crystal is shorter, and the trapping of charges, especially of holes are severe during carrier transportation. The relatively low drift velocity of holes results in a phenomenon of relatively long low-energy tail when the detector detects the ray spectrum, which has certain adverse effect on the counting rate and the spectral resolution. Viewed from the existing manufacture of CdZnTe, the CdZnTe crystal is characterized of a smaller size in crystal growth and non-uniformity of crystal, as well as structural defects. The inconsistency in this crystal will cause a resolution reduction of energy spectrum and a reduction of peak-to-compton ratio of a CdZnTe spectrometer, which adversely affects the identification of spectrum peak of low-energy elements.
Precisely because of the carrier trapping, non-uniformity and defects of the crystal, the output signal of the CdZnTe detector is associated with not only the deposited energy, but also the action location of the ray. The characteristic of spectral resolution is therefore decreased. Currently, the CdZnTe detector designed based on the sensitivity characteristic of single-polarity charge mainly includes: detectors of Parallel Frisch Grid type, Coplanar Frisch Grid type, Hemisphere type, CAPture type, Quasi-hemisphere type, mini-Pixelated type and the like. As restricted by the limitation of the crystal, the performance of the detector cannot be improved further. Especially for a field-enhanced CdZnTe semiconductor detector operating under room temperature and having high energy resolutions and high detection efficiency, in the prior art there is still lack of an efficient method for overcoming inherent crystal defects of the detector and improving the detecting performance further.